Donald Trump has reshuffled his campaign team for the second time in two months as he trails Hillary Clinton in the polls in most key battleground states.

The Republican nominee brought in Stephen Bannon - a combative conservative media executive with no presidential campaign experience - to serve as chief executive of his White House bid.

Pollster Kellyanne Conway, who has known Mr Trump for years and gained his trust during her brief tenure working for the businessman, will serve as campaign manager.

The moves are aimed in part at marginalising campaign chairman Paul Manafort, a long-time Republican operative who pushed Mr Trump to moderate his tone and improve relations with sceptical party officials.

While Mr Manafort maintains his title, Trump allies made clear Mr Bannon will be overseeing the campaign staff and operations.

It is rare for presidential campaigns to undergo this level of tumult at this stage of the election. Wednesday's announcements come less than three months before Mr Trump's face-off with Mrs Clinton.

Mr Trump's standing in the White House race has plunged throughout the summer. He has struggled to offer voters a consistent message, overshadowing formal policy speeches with a stream of controversies, including a public feud with an American Muslim family whose son was killed while serving in the military in Iraq.

According to Republicans close to Mr Trump, the campaign shake-up is aimed at allowing him to fully embrace the aggressive style that helped him win the nomination rather than taking a more restrained, traditional approach.

Mr Bannon's website has been fiercely loyal to Mr Trump for months and sharply critical of Republican leaders, including House Speaker Paul Ryan.

He has also actively promoted false conspiracy theories about Mrs Clinton, and some have then made their way into Mr Trump's remarks.

Ms C onway, a veteran Republican strategist and pollster, joined Mr Trump's campaign earlier this year as a senior adviser and quickly earned his trust.

She said Mr Trump has a history of beating expectations and cannot be counted out.

"August is not October, let alone November," she said.

Mrs Clinton, campaigning in Cleveland, said voters should not be fooled by any Trump efforts to revamp his candidacy.